Simple store for application based on Subject service and your enum for describing application state. There are three ways to use it. Subscribe for latest changes, get value once or subscribe via async pipe in template directly.

npm i ngx-simple-store --save

select(name); // here you can subscribe by name

next(name, value); // setting a new value

getOnce(name); // get what you want without subscription

//Your ./app.module.ts:
import { NgxSimpleStore } from 'ngx-simple-store';

export enum AppState {
  isSideBarOpened = 'isSideBarOpened',
  isDarkTheme = 'isDarkTheme',
  refreshTableState = 'refreshTableState'
}

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    NgxSimpleStoreModule.forRoot(AppState) //our module
  ],
  providers: [],
  bootstrap: [AppComponent]
})

@Component({
  selector: 'app-component',
  template:
  `<button (click)="toggleSideBar()">Toggle Sidebar!</button>`
})
import { NgxSimpleStore } from 'ngx-simple-store';
...
export class AppComponent {
  constructor(private appStore: NgxSimpleStoreService) { }
  
  toggleSideBar() {
    this.appStore.next(AppState.isSideBarOpened, !this.appStore.getOnce(AppState.isSideBarOpened));
  }
}

Three ways to use this service: by subscription, getting once, or using pipe 'async' directly in template (my favorite one, for this you need to do this variable public).

import { NgxSimpleStore } from 'ngx-simple-store';
@Component({
  selector: 'second-component',
  template:
  `<div>
    One more way to use your service!
    {{ appStore.select(AppState.isSideBarOpened) | async }}
  </div>`
})
export class SecondComponent {
  isSideBarOpened;
  constructor(public appStore: NgxSimpleStoreService) {
  
    // subscribe for getting the latest changes
    this.appStore.select(AppState.isSideBarOpened)
        .subscribe(value => console.log(value));
        
    //get value once
    this.isSideBarOpened = this.appStore.getOnce(AppState.isSideBarOpened);
        
  }
}

Sometimes making special services for managing state of sidebar, dark theme of template, width of window, some events between components that are far from each of other and so on is a headache for everyone.

In cases when you need to manage some app states that are used in many places we're doing special service with Subject variable, writing methods for subscribing, adding a new value, getting value once. But when we have a lot of such places it becomes difficult and your code becomes too complicated.

It's just a first version of universal service which you can inject to your component "A", inject to component "B" and use it as common service with common state (like a singleton if you want). I have added an utility function that will convert your enum to individual Subjects by names so it works just as a Subject service that was made for convenient way to work with some common states.

Use distinctUntilChanged for not getting same values (useful in some cases). Use debounceTime for getting latest value in a period of time

this.store
    .select('isOpenedSidebar')
    .pipe(distinctUntilChanged(), debounceTime(500))
    .subscribe(value => {
      this.isSidebarOpen = value;
    });